Goals for 0.4.8

[lausek]

• [x] handles: new value type specifically designed for data inside shared objects
• [x] stdlib: create collection of common functions compilable as shared object modules
  • [X] rough layout
  • [x] more testing
• [x] add new instructions
  • [x] XOr
  • [x] Shl
  • [x] Shr
• [x] iterators
  • [X] implemented
  • [x] more testing
• [x] move define_code from exported macros to tests
• [x] change representation of Call, LCall instructions from (argn, ident_idx) to (ident_idx, argn)
• [x] rename Cast to Conv
• [x] update source code documentation
  • maybe expose ~lovm2_error, lovm2_internals,~ pylovm2 as extern crates in documentation too?
• [x] add lovm2_extend usage documentation
• [x] update pylovm2 on pypi.org
  • ~currently not possible, because lovm2 requires a nightly compiler.~ is possible by changing default compiler to nightly.
• [x] bump lol version

[lausek]

https://lausek.eu/lovm2/2021/02/04/version-0.4.8-released.html

done!